fix(tests): update test assertions for null model in resume /status; drop unused import

Two integration tests expected 'model':'restored-session' in the /status
JSON output but dc4fa55 changed resume mode to emit null for model.
Updated both assertions to assert model is null (correct behavior).

Also remove unused 'estimate_session_tokens' import in compact.rs tests
(surfaced as warning in CI, kept failing CI green noise).

All workspace tests pass.

rust/crates/rusty-claude-cli/tests/resume_slash_commands.rs

@@ -261,7 +261,8 @@ fn resumed_status_command_emits_structured_json_when_requested() {
     let parsed: Value =
         serde_json::from_str(stdout.trim()).expect("resume status output should be json");
     assert_eq!(parsed["kind"], "status");
-    assert_eq!(parsed["model"], "restored-session");
+    // model is null in resume mode (not known without --model flag)
+    assert!(parsed["model"].is_null());
     assert_eq!(parsed["permission_mode"], "danger-full-access");
     assert_eq!(parsed["usage"]["messages"], 1);
     assert!(parsed["usage"]["turns"].is_number());